1. Field of the Invention
The invention relates to a method for making a phosphorus-containing hindered phenol. It more particularly relates to a method involving the conversion of a hindered phenol to a hindered phenol aldehyde and the reaction thereof, without isolation, with a diorganodithiophosphoric acid.
2. Discussion of the Prior Art
Many organic media, including lubricants and greases, hydraulic fluids for brake and transmission systems, resins and plastics for coatings and structural articles, are used under conditions that contribute to their breakdown. Oxidation of lubricants in internal combustion engines is an ever increasing problem, accelerated by the use of higher operating temperatures. The resulting oxidation produced products that may seriously interfere with lubrication.
U.S. Pat. No. 3,644,206 teaches a lubricant composition made by reacting a hindered cyclic aldehyde with a dithioic acid. No art is known, however, that teaches or suggests the method herein.
The compounds produced by the method herein are taught and claimed in U.S. Ser. No. 362,359, filed Mar. 26, 1982. The present method is an improvement over the method used in the application, however, because of the easier operation and because of the reduced production of solid thioaldehyde, polymeric and other undesirable by-products.